Solar central receiver power plants are used to convert the sun's solar thermal energy into electrical energy for connection to a utility grid. Specifically, solar central receiver power plants intercept the sun's thermal energy using a collector system that includes a field of thousands of sun tracking mirrors called heliostats. The heliostats redirect and concentrate the solar thermal energy onto a circular, tower mounted, heat exchanger called a solar receiver. A plurality of planar receiver panels are positioned about the solar receiver for receiving the concentrated solar thermal energy.
The receiver panels each include a plurality of elongated tubes mounted to a suitable strong-back. The elongated tubes terminate at each end in a header. Molten salt coolant at a temperature of approximately 550° F. (287° C.) is pumped up to the solar receiver panels from a cold thermal storage tank located on the ground. The molten salt flows to a first header mounted at a first end of a first receiver panel. The header distributes the molten salt to each of the plurality of tubes in the first panel. As the molten salt flows along the length of the tubes it absorbs the concentrated solar energy.
After the molten salt flows the length of the tubes it is received by a second header located at a second end of the receiver panel. From the second header the salt is piped to a first header of a second receiver panel. The first header of the second panel distributes the molten salt flow to each of the tubes where additional solar energy is absorbed. Molten salt flow continues through subsequent receiver panels in this series pattern until the molten salt is heated to a temperature of approximately 1050° F. (585° C.) in a receiver panel that is last in the series of receiver panels.
From the second header of the last receiver panel the molten salt flows to a hot thermal storage tank on the ground. When the molten salt is needed to generate electricity it is pumped from the hot thermal storage tank to a steam generator where it surrenders heat to produce steam. The steam in turn is used to drive a turbine-generator to generate electricity.
Conventional headers are positioned behind the strong-back to better protect the headers. Positioning the headers behind the strong-back protects the headers from, among other things, weather damage and damage caused by the misdirection of sunlight (known as spillage) upon the headers by the heliostats. Positioning the headers behind the strong-back is also advantageous as it facilitates wrapping the headers with thermal insulation to minimize heat loss from the headers. Headers that face outward toward the concentrated solar flux are difficult to directly insulate due to the high temperature and damage imposed by the solar flux spillage that contacts these headers.
While there are numerous advantages associated with positioning the headers behind the strong-back, this configuration also presents some drawbacks. For example, because the headers are cylinders having opposing ends that each have a 90° surface relative to the main longitudinal length of the header, and the receiver panels are mounted on a cylindrical solar receiver, gaps are created between the headers, tubes, and strong-backs of neighboring receiver panels. Passage of solar energy through these gaps results in a loss of absorbed solar energy and possible damage to the interior components of the solar receiver.
Conventionally, the gaps between the tubes of neighboring receiver panels have been eliminated by bending the tubes in three dimensions such that the tubes extend beyond the width of the headers to fill the gaps. However, bending the tubes in this manner to fill the gaps is undesirable because it is complicated, time consuming, and costly. Thus, there is a need for an improved receiver panel design that eliminates the existence of gaps between the headers, tubes, and strong-backs of neighboring receiver panels and utilizes simplified tube bend designs and techniques.